Electrodeposition of bright zinc, copper, or nickel



United States Patent ELECTRODEPOSITION OF BRIGHT ZINC,

COPPER, OR NICKEL Johannes Fischer, Hanan (Main), Germany, assignor to 'Deutsche Goldund Silher-Scheideanstalt vormals Roessler, Frankfurt am Main, Germany NoDrawing. Application April 23, 1954 Serial No. 425,322

Claims priority, application Germany April 28, 1953 12 Claims. (Cl. 204-49) The present invention relates to an improved electroplating bath for bright plating of metals, such as zinc, nickel and especially copper and copper alloys.

Various types of baths containing brighteners are already known for the bright plating of metals. A large number of organic or inorganic materials have been used as brighteners but such brighteners are often only effective with certain metals or have certain disadvantages which lead to difficulties or completely prevent their use especially in continuous processes or when the electroplating is'carried out at elevated temperatures.

In accordance with the invention it was found that water soluble condensation products of urea or substituted ureas and acrolein or a substituted acroleins such as methyl acrolein and, if desired, other aldehydes act as good brighteners in the bright plating of metals such as copper, zinc, nickel and the like. The urea reaction compounds found suitable for the preparation of the condensation products employed as brighteners according to the invention are of the following general formula R: N C R1 R: \NH2 in which R is oxygen, sulfur, or an imin group, and R and R are hydrogen, alkyl, alkenyl, aryl, aralkyl, or acyl groups of saturated or unsaturated acids.

Urea acrolein condensation products of this type which are especially suited for the purposes of the invention are described in German Patents Nos. 554,552, 745,422, and 748,842 as well as in French Patents Nos. 879,957, 884,- 091, and 985,231. by condensation in the presence of hydroxyl group con taining compounds, have been found particularly suitable for the purposes of the invention.

It was found that acrolein or an a substituted acrolein must be present in the aldehyde components of the urea or substituted urea aldehyde resins in order that the condensation products are active as brighteners. However in many instances the acrolein or a substituted acroleins can be only a minor portion of the aldehyde component of the condensation product.

Especially good results are obtained with respect to the surface character of the metal electrodeposits obtained with baths containing a brightener according to the invention it the deposit is from alkaline baths and above all from cyanide baths. However, contrary to many of the known brighteners the urea condensation products employed according to the invention can also be employed in acidic baths.

The quantity of the condensation product added as a brightener to the electrolytic baths should be at least 0.5 g./l. and can otherwise vary within wide limits. In general smaller quantities are required in acidic baths than in alkaline baths .in which advantageously 3.5. to 35 g./l. of the condensation products are employed.

Such products which are produced Very good bright effects can be obtained when the amount of condensation product added lies between 6 and 15, for examp1e, 10 g./l. In alkaline electroplating baths containing less than 3.5 g./l. of condensation product, it is sometimes advisable to add other known brighteners, such as, for example, potassium thiocyanate.

The electroplating baths according to the invention can in addition to the urea condensation products, also contain water soluble polyglycol esters preferably those of fatty acids containing 4 to 15 carbon atoms. The polyglycol radical preferably is one produced from 5 to 25 moles of ethylene oxide. Besides being water soluble the polyglycol esters should be stable in alkalies up to 70 C. and at pH values up to about 13. The quantities of such polyglycol esters added can be between 2 and 20 g./l., preferably 5 and 10 g./l. of bath.

It was also found advantageous to 'add a small proportion of an alkali metal xanthate to the electroplating baths according to the invention as the range of brightness can be increased thereby. The quantity of such xanthate addition can forexample be 0.01 to 1.0 g./l., preferably, 0.05 to 0.2 g./l. of bath.

In selecting the operating conditions for the electroplating baths according to the invention, consideration should be given to. the fact that the brightness range increases with increase in the quantity of brightener contained in the baths and that the. maximum brightness at current densities between 1 and 10 amp./dm. is displaced toward the higher current densities with increasing brightener content of the baths. Even though the selection of the. most favorable current density is dependent upon the electroplated metal, bath temperature as well as the brightener content, it has been found desirable wherever possible to employ current densities of 1 to 2 amp./dm. for acid electrolytes and current densities of 2 to 5 amp./dm. for alkaline electrolytes. In many instances especially when alkaline electroplating baths are employed it has been found desirable to select bath temperatures of 50 C. and over, as at lower temperatures blocking anode fibers may form. The brightness of the metal deposited can be enhanced by movement of the baths. For this purpose, in general a simple quiet movement of the cathode suffices.

Although electrolytic baths containing organic brighteners ordinarily are not suited or only poorly suited for electroplating with periodically reversing current it was unexpectedly found that periodically reversing current can be employed with success in baths according to the invention especially when thick platings are desired. For example, plating periods of about 25 seconds and deplating periods of about 5 seconds can be employed.

The following are, by way of example, several ureaor substituted urea-acrolein condensation products and their method of production which are suitable as brighteners in electroplating baths according to the invention:

(a) 60 parts by weight of urea were mixed with 60 parts by weight of water, parts by weight of hexamethylenetetramine and 11 parts by weight of acrolein and the mixture gradually heated to 60 C. and maintained at this temperature for about 20 minutes. Thereafter parts by weight of triethylene glycol were added and the mixture was heated to 150 C. for an hour. After cooling an orange colored resin solution which is easily dissolved in 'waterwas obtained.

(b) 3 parts by weight of sodium acetate were added to a'mixture of 60 parts by weight of guanidine, 20 parts by weight of water, 44 parts by weight of acetaldehyde and 14 parts by v /eight. 9i acrolein. .The. temperature rose to 32 C. after 3 minutes and, then remained con stant. ,Ihereatfet the temaerature was raised l w y ing 10 minutes to 60 C. and then held at this temperature for minutes. After addition of 62 parts by I weight of ethylene glycol to the heterogeneous reaction solution, the mixture was heated for 1 hour at 140 C. and then cooled under reflux. A condensation product was obtained which faintly smelled of acetone and which was easily dissolved in water in all proportions.

(c) 3 parts by weight of a normal aqueous NaOH solution were added to a mixture of 60 parts by weight of urea, 72 parts by weight of methylacrolein, 248 parts by weight of ethylene glycol and 82.5 parts by weight of paraformaldehyde and the reaction liquid heated under reflux on an oil bath for 2 hours at 120 C. A solution of an oily resin was obtained which is soluble in water.

(d) 2 parts by weight of a normal aqueous NaOH solution were mixed with 88 parts by weight of dimethyl urea and 42 parts by weight of acrolein and the mixture was heated to 50 C. Thereafter the temperature was raised during 15 minutes to 80 Cland a viscous solution of a transparent, water soluble resin was obtained.

The following examples will serve to illustrate'several modifications of electroplating baths according to the invention employing the above condensation products as well as their use in electroplating.

I Example 1 An aqueous potassium cyanide containing copper plating bath of the following composition was prepared:

Cu as K Cu(CN) KGN l5 KOH 30 Condensation product (a) 10.5 Polyglycol ester of moles ethylene oxide and a mixture of fatty acids containing 4-9 carbon atoms 6 Sodium xanthate 0.3

When this bath was employed to copper plate a pre cleaned steel base at 70 C. and at a current density between 4 and 5 amp./dm. a bright copper plate is obtained which can be plated with nickel in the usual nickel plating baths without further pretreatment.

Good bright copper platings were also obtained with this bath at the same temperature when employing a periodically reversing current of 40 second electrodepositing and 10 second anodizing periods at current densities between 5 and 10 amp./dm.

Example 2 An aqueous sodium cyanide containing zinc plating bath of the following composition was prepared:

G./l. Zn(CN) V 60 NaCN 40 NaOH 74 Condensation product (a) 8 An aqueous acidic nickel plating bath of the following composition was prepared;

G./l. NiS0 120! NiCL Boric acid 30 Condensation product (a).. l

The pH value of such bath was about 3.

When this bath was employed at a temperature of 40 C. and current densities between 1' and 2 amp./dm. bright nickel platings were obtained.

Example 4 An aqueous acidic copper plating bath of the following composition was prepared:

CuSO 125 H 30 Condensation product (a) 7 This bath was employed with a moving cathode at a temperature of about 20 C. and a current density of about 7 arnp./dm. and gave very bright hard copper platings.

Example 5 An aqueous copper plating bath of the following composition was prepared:

G./l. Copper (as K Cu(CN) 45 KCN 8 KOH 10 Polyglycol ester of 20 moles ethylene oxide and a mixture of fatty acids containing 4-9 carbon atoms 8 Condenstation product (b) 14 This bath gave good bright copper platings at a bath temperature about 60 C. and current densities of from 2 to 3 amp./dm.

Example 6 An aqueous brass plating bath of the following com position was prepared:

7 11. CuCn 26 Zn(CN) ll NaCN 45 Polyglycol ester of 20 moles ethylene oxide and a mixture of fatty acids containing 4-9 carbon atoms 3 Condensation product (d) 7 This bath gave uniform firmly adhering brass platings at bath temperatures of about 60 C. and current densities of 1 to 2 amp./dm.

Example 7 An aqueous copper plating bath of the followingcornposition was prepared:

G./l. CuCN 22.5

NaCN V 34.0 Na CO 15 of the metal to be deposited which contains as a bright ener at least 0.5 gram per liter of a condensation product of an unsaturated aldehyde selected from the group consisting of acrolein and its alpha substitution products, and a urea of the general formula V R: 02R: R:

NH: wherein R is selected from the group consisting of oxygen, sulfur and imin radicals and R, and R are each selected from the group consisting of hydrogen, alkyl, alkenyl, aryl, aralkyl and acyl groups of saturated and unsaturated acids.

2. A bright metal electroplating bath according to claim 1 in which the quantity of said condensation product is 3.5 to 35 grams per liter of bath.

-3. A bright metal electroplating bath according to claim 1 in which the quantity of said condensation product is 6 to grams per liter of bath.

4. A bright metal electroplating bath according to claim 1 comprising in addition 2 to grams per liter of bath of a water soluble polyglycol ester of a fatty acid containing 4 to 15 carbon atoms.

5. A bright metal electroplating bath according to claim 1 comprising in addition 5 to 10 grams per liter of bath of a water soluble polyglycol ester of a fatty acid containing 4 to 15 carbon atoms.

6. A bright metal electroplating bath according to claim 1 comprising in addition 0.01 to 1 gram per liter of bath of an alkali metal xanthate.

7. A bright metal electroplating bath according to claim 1 comprising in addition 0.05 to 0.2 gram per liter of bath of an alkali metal xanthate.

8. A bright metal plating bath according to claim 1' containing at least one other brightener in addition to the condensation product.

9. A bright metal plating bath according to claim 1 in which said condensation product is one that has been produced inthe presence of a compound containing hydroxyl groups.

10. A method for producing a bright metal electrodeposit of a metal selected from the group consisting of zinc, copper and nickel which comprises electroplating a material in an electroplating bath comprising an aqueous electrolyte of the metal to be deposited which contains as a brightener at least 0.5 gram per liter of a condensation product of an unsaturated aldehyde selected from the group consisting of acrolein and its alpha substitution products, and a urea of the general formula /R: Gilli Ra NH, wherein R is selected from the group consisting of oxygen, sulfur and imin radicals and R and R are each selected from the group consisting of hydrogen, alkyl, alkenyl, aryl, aralkyl and acyl groups of saturated and unsaturated acids.

11. A method according to claim 10 in which said electroplating bath is maintained at a temperature above C.

12. A method according to claim 10 in which said electroplating is carried out with periodically reversing current.

References Cited in the file of this patent UNITED STATES PATENTS 2,101,581 Henricks Dec. 7, 1937 2,146,439 Oplinger Feb. 7, 1939 2,451,341 Iernstedt Oct. 12, 1948 2,457,152 Hoffman Dec. 28, 1948 2,677,654 Chester et al. May 4, 1954 

1. A BRIGHT METAL ELECTROPLATING BATH FOR ELECTRODEPOSITING A METAL SELECTED FROM THE GROUP CONSISTING OF ZINC, COPPER AND NICKEL COMPRISING AN AQUEOUS ELECTROLYTE OF THE METAL TO BE DEPOSITED WHICH CONTAINS AS A BRIGHTENER AT LEAST 0.5 GRAM PER LITER OF A CONDENSATION PRODUCT OF AN INSATURATED ALEDHYDE SELECTED FROM THE GROUP CONSISTING OF ACROLEIN AND ITS ALPHA SUBSTITUTION PRODUCTS, AND A UREA OF THE GENERAL FORMULA 